Sub-carrier estimation method and apparatus in multi-carrier communication system

ABSTRACT

Provided are a sub-carrier estimation method in a multi-carrier communication system and an apparatus. The method includes: receiving a data frame transmitted by a transmitting end, and extracting a training sequence from the data frame; performing fast Fourier transform operation on the training sequence and a preset reference sequence, respectively, to obtain frequency domain data of the training sequence and frequency domain data of the reference sequence, and conjugately multiplying the two kinds of frequency domain data; extracting real part of conjugate multiplication result; averaging values in each column of an M×N array, respectively, to obtain an output array of 1 row and N columns; and estimating, according to the value in each column of the output array of 1 row and N columns, whether valid data is transmitted over N sub-carriers corresponding to the output array of 1 row and N columns.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/CN2017/078536 filed on Mar. 29, 2017, which claims the prioritybenefit of China Patent Application No. 201710066232.0 filed on Feb. 6,2017. The contents of the above identified applications are incorporatedherein by reference in their entireties.

TECHNICAL FIELD

The present disclosure relates to the field of communications and, inparticular, to a sub-carrier estimation method in a multi-carriercommunication system and an apparatus.

BACKGROUND

Multi-carrier modulation techniques have strong anti-interferenceability and high spectrum utilization efficiency, which can effectivelyresist frequency selective fading and have been widely used in broadbandcommunication systems. Orthogonal frequency division multiplexing(Orthogonal Frequency Division Multiplexing, OFDM) is one of themulti-carrier modulation techniques. It is implemented with lowcomplexity, and can eliminate inter-symbol interference and effectivelyresist multipath effect. Therefore, it is widely used in power linecommunication systems and wireless communication systems.

During practical use, in a multi-carrier communication system, amoderate amount of sub-carriers and frequency bands with lessinterference are often selected to transmit valid data, instead offrequency bands with large interference. The accuracy of the estimationon the number of sub-carriers and positions of the sub-carriers by thereceiving end directly affects subsequent demodulation operations.

In the prior art, the sub-carrier estimation is usually made using anautocorrelation method, while the accuracy of the estimation on thenumber of sub-carriers and the positions of the sub-carriers is poor. Inorder to improve the accuracy of the sub-carrier estimation, a KS(Kolmogorov-Smirnov) test method or a higher-order cyclic cumulantmethod is introduced in some sub-carrier estimation methods, resultingin a very large computational burden for the sub-carrier estimation.

SUMMARY

The technical problem to be solved in the present disclosure is toimprove accuracy of sub-carrier estimation while the sub-carrierestimation is implemented with low complexity.

To solve the above technical problem, an embodiment of the presentdisclosure provides a sub-carrier estimation method in a multi-carriercommunication system, including: receiving a data frame transmitted by atransmitting end, and extracting a training sequence from the dataframe; performing a fast Fourier transform operation on the trainingsequence and a preset reference sequence, respectively, to obtainfrequency domain data of the training sequence and frequency domain dataof the reference sequence, and conjugately multiplying the frequencydomain data of the training sequence by the frequency domain data of thereference sequence; extracting a real part of a conjugate multiplicationresult, where the real part of the conjugate multiplication result is anM×N array, with M being the number of symbols of the training sequence,and N being the number of points of the fast Fourier transformoperation; averaging all values in each column of the M×N array,respectively, to obtain an output array of 1 row and N columns; andestimating, according to a value in each column of the output array of 1row and N columns, whether valid data is transmitted over N sub-carrierscorresponding to the output array of 1 row and N columns.

Optionally, the estimating, according to the value in each column of theoutput array of 1 row and N columns, whether the valid data istransmitted over the N sub-carriers corresponding to the output array of1 row and N columns includes: sequentially comparing values in theoutput array of 1 row and N columns with a first threshold that ispreset; when an l^(th) value in the output array of 1 row and N columnsis greater than the first threshold, it is determined that the validdata is transmitted over an l^(th) sub-carrier of the N sub-carriers;and when the l^(th) value in the output array of 1 row and N columns isnot greater than the first threshold, it is determined that no validdata is transmitted over the l^(th) sub-carrier of the N sub-carriers;where 1≤l≤N.

Optionally, the N sub-carriers are divided into k sub-carrier groups,sub-carriers in any of the sub-carrier groups are adjacent to each otherin a frequency domain, and there is no intersection between any two ofthe sub-carrier groups; the estimating, according to the value in eachcolumn of the output array of 1 row and N columns, whether the validdata is transmitted over the N sub-carriers corresponding to the outputarray of 1 row and N columns includes: acquiring, from the output arrayof 1 row and N columns, values corresponding to all sub-carriers in eachsub-carrier group, respectively; and estimating whether the valid datais transmitted over all sub-carriers in the each sub-carrier group,respectively.

Optionally, the estimating whether the valid data is transmitted overall sub-carriers in the each sub-carrier group, respectively, includes:calculating an average value for values corresponding to allsub-carriers in the each sub-carrier group, and comparing the averagevalue with a second threshold that is preset; when the average value forthe values corresponding to all sub-carriers in the each sub-carriergroup is greater than the second threshold, it is determined that thevalid data is transmitted over all sub-carriers in the each sub-carriergroup; and when the average value for the values corresponding to allsub-carriers in the each sub-carrier group is not greater than thesecond threshold, it is determined that no valid data is transmittedover any of the sub-carriers in the each sub-carrier group.

Optionally, after estimating whether the valid data is transmitted overthe N sub-carriers corresponding to the output array of 1 row and Ncolumns, the method further includes: counting the number ofsub-carriers, over which the valid data is transmitted, in the Nsub-carriers.

Optionally, before extracting the training sequence from the data frame,the method further includes: performing synchronization processing ondata in the data frame.

Optionally, the training sequence includes any one of: a preamblesequence in the data frame for synchronization; or a data sequence thatis preset in the data frame.

An embodiment of the present disclosure further provides a sub-carrierestimation apparatus in a multi-carrier communication system, including:a receiving unit, configured to receive a data frame transmitted by atransmitting end; a training sequence extracting unit, configured toextract a training sequence from the data frame; a fast Fouriertransform operation unit, configured to perform a fast Fourier transformoperation on the training sequence and a preset reference sequence,respectively, to obtain frequency domain data of the training sequenceand frequency domain data of the reference sequence; a multiplicationunit, configured to conjugately multiply the frequency domain data ofthe training sequence by the frequency domain data of the referencesequence; a real part extracting unit, configured to extract a real partof a conjugate multiplication result, where the real part of theconjugate multiplication result is an M×N array, with M being the numberof symbols of the training sequence, and N being the number of points ofthe fast Fourier transform operation; a calculation unit, configured toaverage all values in each column of the M×N array, respectively, toobtain an output array of 1 row and N columns; and an estimating unit,configured to estimate, according to a value in each column of theoutput array of 1 row and N columns, whether valid data is transmittedover N sub-carriers corresponding to the output array of 1 row and Ncolumns.

Optionally, the estimating unit is configured to sequentially comparevalues in the output array of 1 row and N columns with a first thresholdthat is preset; when an l^(th) value in the output array of 1 row and Ncolumns is greater than the first threshold, it is determined that thevalid data is transmitted over an l^(th) sub-carrier of the Nsub-carriers; and when the l^(th) value in the output array of 1 row andN columns is not greater than the first threshold, it is determined thatno valid data is transmitted over the l^(th) sub-carrier of the Nsub-carriers; where 1≤l≤N.

Optionally, the N sub-carriers are divided into k sub-carrier groups,sub-carriers in any of the sub-carrier groups are adjacent to each otherin a frequency domain, and there is no intersection between any two ofthe sub-carrier groups; the estimating unit is configured to: acquire,from the output array of 1 row and N columns, values corresponding toall sub-carriers in each sub-carrier group, respectively; and estimatewhether the valid data is transmitted over all sub-carriers in the eachsub-carrier group, respectively.

Optionally, the estimating unit is further configured to: calculate anaverage value for values corresponding to all sub-carriers in the eachsub-carrier group, and compare the average value with a second thresholdthat is preset; when the average value for the values corresponding toall sub-carriers in the each sub-carrier group is greater than thesecond threshold, it is determined that the valid data is transmittedover all sub-carriers in the each sub-carrier group; and when theaverage value for the values corresponding to all sub-carriers in theeach sub-carrier group is not greater than the second threshold, it isdetermined that no valid data is transmitted over any of thesub-carriers in the each sub-carrier group.

Optionally, the sub-carrier estimation apparatus in the multi-carriercommunication system further includes: a counting unit, configured tocount the number of sub-carriers, over which the valid data istransmitted, in the N sub-carriers.

Optionally, the sub-carrier estimation apparatus in the multi-carriercommunication system further includes: a synchronization processingunit, configured to perform synchronization processing on data in thedata frame before the training sequence extracting unit extracts thetraining sequence from the data frame.

Optionally, the training sequence includes any one of: a preamblesequence in the data frame for synchronization; or a data sequencepreset in the data frame.

Compared with the prior art, the technical solutions in embodiments ofthe present disclosure have the following beneficial effects:

An M×N array is obtained by conjugately multiplying a training sequenceextracted from a data frame by a preset reference sequence andextracting a real part of the resulting product. An output array of 1row and N columns is obtained by averaging values in each column of theM×N array, and it is estimated whether valid data is transmitted over Nsub-carriers corresponding to the output array of 1 row and N columns.There is no need to introduce a complicated mathematical model inestimating whether valid data is transmitted over the sub-carriers.Whether the valid data is transmitted over the sub-carriers isattainable provided that a simple operation is performed. Therefore, acomputation burden is effectively reduced for the sub-carrierestimation. The output array of 1 row and N columns is obtained byextracting the real part of the conjugate multiplication result, andaveraging values corresponding to each column. It is estimated,according to the values in each column of the output array of 1 row andN columns, whether the valid data is transmitted over the Nsub-carriers. Therefore, the accuracy of the sub-carrier estimation canbe improved.

Further, the N sub-carriers are divided into k sub-carrier groups toestimate whether the valid data is transmitted over the respectivesub-carrier groups. When it is determined that the valid data istransmitted over one sub-carrier group, it is determined that the validdata is transmitted over all sub-carriers in the sub-carrier group.Therefore, the accuracy and efficiency of the sub-carrier estimation canbe improved.

Further, by counting the number of all sub-carriers of the Nsub-carriers over which the valid data is transmitted, it is possible toaccurately know how many sub-carriers the valid data is currentlytransmitted over.

In addition, using a preamble sequence in the data frame forsynchronization as the training sequence can reduce the length of thedata frame and improve data transmission efficiency.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a flow chart of a sub-carrier estimation method in amulti-carrier communication system according to an embodiment of thepresent disclosure; and

FIG. 2 is a schematic structural diagram of a sub-carrier estimationapparatus in a multi-carrier communication system according to anembodiment of the present disclosure.

DESCRIPTION OF EMBODIMENTS

In the prior art, the sub-carrier estimation is usually made using anautocorrelation method. However, in the event of using theautocorrelation sub-carrier estimation method in low signal to noiseratio environment, the accuracy of the estimation on the number ofsub-carriers and the positions of the sub-carriers would be poor. Inorder to improve the accuracy of the sub-carrier estimation, a KS(Kolmogorov-Smirnov) test method or a higher-order cyclic cumulantmethod is introduced in some sub-carrier estimation methods, resultingin a large computational burden and a high computational complexity inthe sub-carrier estimation.

In an embodiment of the present disclosure, an M×N array is obtained byconjugately multiplying a training sequence extracted from a data frameby a preset reference sequence and extracting a real part of theresulting product. An output array of 1 row and N columns is obtained byaveraging values in each column of the M×N array, and it is estimatedwhether valid data is transmitted over N sub-carriers corresponding tothe output array of 1 row and N columns. There is no need to introduce acomplicated mathematical model in estimating whether valid data istransmitted over the sub-carriers. Whether the valid data is transmittedover the sub-carriers is attainable provided that a simple operation isperformed. Therefore, a computation burden is effectively reduced forthe sub-carrier estimation. The output array of 1 row and N columns isobtained by extracting the real part of the conjugate multiplicationresult, and averaging values corresponding to each column. It isestimated, according to the value in each column of the output array of1 row and N columns, whether the valid data is transmitted over the Nsub-carriers. Therefore, the accuracy of the sub-carrier estimation canbe improved.

The described objectives, features and beneficial effects of the presentdisclosure will become more apparent from the detailed description ofembodiments of the present disclosure.

An embodiment of the present disclosure provides a sub-carrierestimation method in a multi-carrier communication system, of whichspecific steps will be described hereunder in detail with reference toFIG. 1.

Step S101, receiving a data frame transmitted by a transmitting end, andextracting a training sequence from the data frame.

In a specific implementation, after receiving the data frame transmittedby the transmitting end, a receiving end can first performsynchronization processing on the received data in the data frame. Afterthe synchronization processing is completed, the training sequence isextracted from the data frame.

When generating the data frame, the transmitting end can add anindependent data sequence in the data frame in advance as the trainingsequence. That is to say, in addition to the valid data that needs to betransmitted, a preset training sequence is also included in the dataframe transmitted by the transmitting end.

After the data frame is received and the synchronization is completed bythe receiving end, the training sequence can be extracted from the dataframe. In ideal channel conditions, when the data frame is not subjectto interference during a channel transmission, there would be no changein the data of the training sequence from the data frame.

When the data sequence is added in the data frame as the trainingsequence, the length of the data frame will be relatively long. Inanother embodiment of the present disclosure, a preamble sequence forsynchronization in the data frame is used as the training sequence.Since the preamble sequence needs to be set in each data frame, thelength of the data frame can be reduced by reusing the preamblesequence.

Step S102, performing a fast Fourier transform on the training sequenceand a preset reference sequence, respectively, to obtain frequencydomain data of the training sequence and frequency domain data of thereference sequence, and conjugately multiplying the frequency domaindata of the training sequence by the frequency domain data of thereference sequence.

In a specific implementation, a reference sequence can be preset at thereceiving end, and the reference sequence is the same as the trainingsequence that is set at the transmitting end.

The training sequence extracted from the data frame is time domain data,and the time domain data of the training sequence can be converted intofrequency domain data of the training sequence via a fast Fouriertransform (Fast Fourier Transform, FFT) operation. Accordingly, timedomain data of the reference sequence can be converted into frequencydomain data of the reference sequence via the FFT operation. After thefrequency domain data of the training sequence and the frequency domaindata of the reference sequence are obtained, they are conjugatelymultiplied.

In an embodiment of the present disclosure, the frequency domain data ofthe training sequence is set to rx_data, the frequency domain data ofthe reference sequence is set to ref_data, and the conjugatemultiplication result mul_data obtained by conjugately multiplying thesetwo is:

mul_data=rx_data*conj(ref_data);  (1)

In the formula (1), conj (ref_data) is a conjugate of ref_data.

Step S103, extracting a real part of the conjugate multiplicationresult.

In ideal channel conditions, the training sequence extracted from thedata frame is the same as the reference sequence that is preset at thereceiving end, that is, rx_data is equal to ref_data. Supposeref_data=a+b*j, then:

mul_data=(a+b*j)*(a−b*j)=a ² +b ²;  (2)

where j=sqrt(−1).

However, during practical use, the data frame will be subject tointerference and other influence during a channel transmission process,resulting in a certain difference between the actually extractedtraining sequence and the reference sequence. Therefore, the calculatedvalue of mul_data includes a real part and an imaginary part, ratherthan a pure real number. In an embodiment of the present disclosure,after mul_data is obtained through the calculation, its real part istaken.

In a specific implementation, the number of symbols of the trainingsequence is set to M, and the number of points of the FFT is set to N,then the extracted real part of the conjugate multiplication result isan array of M rows and N columns.

Step S104, averaging all values in each column of the M×N array,respectively, to obtain an output array of 1 row and N columns.

In a specific implementation, for each column of the M×N array, allvalues in each column are summed up, and the obtained sum value isdivided by M to obtain an average value for each column, thus the outputarray of 1 row and N columns can be obtained.

Step S105, estimating, according to the value in each column of theoutput array of 1 row and N columns, whether valid data is transmittedover N sub-carriers corresponding to the output array of 1 row and Ncolumns.

In a specific implementation, for the value in each column of the outputarray of 1 row and N columns, that is, for each value in the outputarray of 1 row and N columns, it is compared with a first threshold thatis preset. When the i^(th) value in the output array of 1 row and Ncolumns is greater than the first threshold, it can be determined thatvalid data is transmitted over the i^(th) sub-carrier of the Nsub-carriers. Conversely, when the i^(th) value in the output array of 1row and N columns is not greater than the first threshold, it can bedetermined that no valid data is transmitted over the i^(th) sub-carrierof the N sub-carriers.

For example, in the case of N=512, when the 1^(st) value in the outputarray of 1 row and 512 columns is greater than the first threshold, itcan be determined that valid data is transmitted over the 1^(st)sub-carrier, that is, sub-carrier 1. When the 2^(nd) value in the outputarray of 1 row and 512 columns is not greater than the first threshold,it can be determined that no valid data is transmitted over the 2^(nd)sub-carrier, that is, sub-carrier 2.

In a specific implementation, when the valid data is transmitted overthe sub-carriers, the training sequence will be simultaneouslytransmitted. Since it is predefined that the training sequence is thesame as the reference sequence at the receiving end, the real part forthe product obtained from a conjugate multiplication of the frequencydomain data of the training sequence by the frequency domain data of thereference sequence is usually relatively large. Therefore, when thevalid data is transmitted over the sub-carriers, the real part value ofthe corresponding conjugate multiplication result is relatively large.Hence, whether the valid data is transmitted over the sub-carriers canbe determined by comparing the real part value of the conjugatemultiplication result with the first threshold that is preset.

Thus, it can be seen that there is no need to introduce a complicatedmathematical model in estimating whether valid data is transmitted overthe sub-carriers. Whether the valid data is transmitted over thesub-carriers is attainable provided that a simple operation isperformed. Therefore, a computation burden is effectively reduced forthe sub-carrier estimation. The M×N array is obtained by extracting thereal part of the conjugate multiplication result, and the output arrayof 1 row and N columns is obtained by averaging values corresponding toeach column. It is estimated, according to the value in each column ofthe output array of 1 row and N columns, whether the valid data istransmitted over the N sub-carriers. Therefore, the accuracy of thesub-carrier estimation can be improved.

In a specific implementation, the value of the number of symbols M ofthe training sequence may be set according to actual applicationscenarios. The larger the M, the higher the accuracy with regard toestimating whether the valid data is transmitted over the estimatedsub-carriers. Accordingly, since the training sequence at thetransmitting end is relatively long, the data transmission efficiency atthe transmitting end will be reduced. The smaller the M, the lower theaccuracy with regard to estimating whether the valid data is transmittedover the estimated sub-carriers. Accordingly, since the trainingsequence at the transmitting end is relatively short, the datatransmission efficiency at the transmitting end will be higher. Duringpractical use, a trade-off can be made between the data transmissionefficiency at the transmitting end and the accuracy of the estimation.

In a specific implementation, the transmitting end can also group the Nsub-carriers according to an actual application scenario to obtain ksub-carrier groups. Respective sub-carrier groups are independent ofeach other, there is no intersection between any two of the sub-carriergroups, and adjacent sub-carriers in each sub-carrier group are adjacentto each other in a frequency domain. When performing modulation datamapping, the transmitting end performs the modulation data mapping inunit of sub-carrier groups; that is to say, valid data is transmittedover all sub-carriers in a sub-carrier group, or no valid data istransmitted over any of the sub-carriers in a sub-carrier group.

When grouping the N sub-carriers, in order to facilitate a hardwareimplementation, the N sub-carriers may be equally divided into ksub-carrier groups, and for the number of sub-carriers in eachsub-carrier group, n=N/k. Also, it can be understood that the number ofsub-carriers in respective sub-carrier groups may vary in grouping the Nsub-carriers.

For example, in the case of N=512, 512 sub-carriers are equally dividedinto 16 sub-carrier groups, and for the number of sub-carriers in eachsub-carrier group, n=512/16=32. The 1^(st) sub-carrier group includessub-carriers 1 to 32, the 2^(nd) sub-carrier group includes sub-carriers33 to 64, and similarly, the 16^(th) sub-carrier group includessub-carriers 481 to 512.

After the output array of 1 row and N columns is obtained, the outputarray of 1 row and N columns corresponds to N sub-carriers. The outputarray of 1 row and N columns is accordingly divided into k groupsaccording to the number of sub-carrier groups. All the data in eachgroup of the k groups is averaged, respectively, to obtain k averagevalues, and an output array of 1 row and k columns is formed.

For example, if 512 sub-carriers are equally divided into 16 sub-carriergroups, then the output array of 1 row and 512 columns is equallydivided into 16 groups, and values in the output array of 1 row and 512columns are sequentially V_(L1)˜V_(L512). V_(L1)˜V_(L32) in the outputarray of 1 row and 512 columns are averaged to obtain an average valuecorresponding to the 1^(st) sub-carrier group, and V_(L1)˜V_(L32) arevalues in the output array of 1 row and N columns corresponding tosub-carriers 1˜32. V_(L33)˜V_(L64) in the output array of 1 row and 512columns are averaged to obtain an average value corresponding to the2^(nd) sub-carrier group, and V_(L33)˜V_(L64) are values in the outputarray of 1 row and N columns corresponding to sub-carriers 33˜64.Similarly, average values corresponding to the remaining 14 sub-carriergroups are calculated, respectively, and an output array of 1 row and 16columns is obtained.

After the output array of 1 row and k columns is obtained, the value ineach column of the output array of 1 row and k columns can be comparedwith a second threshold that is preset. When the value in the m^(th)column of the output array of 1 row and k columns is greater than thesecond threshold, it can be determined that valid data is transmittedover all of the n sub-carriers in the m^(th) sub-carrier group; when thevalue in the m^(th) column of the output array of 1 row and k columns isnot greater than the second threshold, it can be determined that novalid data is transmitted over any of the n sub-carriers in the m^(th)sub-carrier group.

For example, if 512 sub-carriers are equally divided into 16 sub-carriergroups, an output array of 1 row and 16 columns can be obtained. In theoutput array of 1 row and 16 columns, if the value in the 1^(st) columnis greater than the second threshold, it can be determined that validdata is transmitted over all sub-carriers in the 1^(st) sub-carriergroup, that is, valid data is transmitted over sub-carriers 1˜32.

For another example, in the output array of 1 row and 16 columns, if thevalue in the 2^(nd) column is not greater than the second threshold, itcan be determined that no valid data is transmitted over any ofsub-carriers in the 2^(nd) sub-carrier group, that is, no valid data istransmitted over any of sub-carriers 33˜64.

It can be derived at one time whether valid data is transmitted overmultiple sub-carriers by grouping the N sub-carriers, respectivelycalculating the real part average value of the conjugate multiplicationresult corresponding to each sub-carrier in each group, then averagingthe real part average values of the conjugate multiplication resultscorresponding to each sub-carrier group, and comparing the obtainedresults with the second threshold, thus the accuracy and efficiency ofthe sub-carrier estimation can be improved.

In a specific implementation, in the case of grouping the Nsub-carriers, if the number of groups k is relatively small, the numberof sub-carriers in each group is relatively large when the Nsub-carriers are equally divided. When the number of sub-carriers ineach group is relatively large, the sub-carrier estimation has a higheraccuracy, and the sub-carrier estimation has a higher efficiency,however, there is a lower flexibility in using the sub-carriers.

In the case of grouping the N sub-carriers, if the number of groups k isrelatively large, the number of sub-carriers in each group is relativelysmall when the N sub-carriers are equally divided. When the number ofsub-carriers in each group is relatively small, the sub-carrierestimation has a lower accuracy, and the sub-carrier estimation has alower efficiency, however, there is a higher flexibility in using thesub-carriers.

Therefore, the number of groups k may be selected according to actualusage requirements. If requirements on accuracy and efficiency arerelatively high for the sub-carrier estimation, then k may take asmaller value, for instance, k=8 or k=16. If requirements on flexibilityfor the sub-carrier usage is relatively high, then k may take a largevalue, for example, k=32 or k=64. During practical use, k may also takeother values, for details, description is omitted herein.

In an embodiment of the present disclosure, it can be predefined thatthe first threshold may be equal to the second threshold, or the firstthreshold may be unequal to the second threshold, depending on theactual application scenario.

In a specific implementation, after estimating which sub-carriers thevalid data is transmitted over, the number of all sub-carriers of the Nsub-carriers over which the valid data is transmitted can also becounted. Each of the estimation results of all the estimatedsub-carriers over which the valid data is transmitted may be set to 1,and each of the estimation results of all the estimated sub-carriersover which no valid data is transmitted is set to 0, then a binarysequence of length N can be obtained. By counting the number of 1 in thebinary sequence of length N, the number of sub-carriers over which thevalid data is transmitted can be known.

In an embodiment of the present disclosure, a bit by bit addition isperformed on the binary sequence of length N using an accumulator, andthe obtained sum value is the number of sub-carriers over which thevalid data is transmitted.

For example, N=512. If it is estimated that valid data is transmittedover sub-carrier 1, then the estimation result of the sub-carrier 1 maybe set to 1. If it is estimated that no valid data is transmitted oversub-carrier 2, then the estimation result of the sub-carrier 2 may beset to 0. Similarly, a binary sequence of 512 bits in length isobtained, and the first two bits of the binary sequence are 10.

Steps S103-S105 provided in the above embodiments of the presentdisclosure will be described hereunder by way of examples.

Assume M=4 and N=512, reference may be made to Table 1 below for a realpart of the extracted conjugate multiplication result.

TABLE 1 S_(1,1) S_(1,2) S_(1,3) . . . S_(1,31) S_(1,32) S_(1,33) . . .S_(1,512) S_(2,1) S_(2,2) S_(2,3) . . . S_(2,31) S_(2,32) S_(2,33) . . .S_(2,512) S_(3,1) S_(3,2) S_(3,3) . . . S_(3,31) S_(3,32) S_(3,33) . . .S_(3,512) S_(4,1) S_(4,2) S_(4,3) . . . S_(4,31) S_(4,32) S_(4,33) . . .S_(4,512)

In Table 1, there is an array of 4 rows and 512 columns, where S_(i,l)represents the real part of the conjugate multiplication result for thel^(th) sub-carrier of the i^(th) symbol, 1≤i≤4, 1≤l≤512.

All values of each column in Table 1 are averaged, respectively, toobtain 512 average values, where the average value of the l^(th) columnis: V_(Ll)=(S_(1,l)+S_(2,l)+S_(3,l)+S_(4,l))/4.

Reference may be made to Table 2 below for an output array of 1 row and512 columns.

TABLE 2 V_(L1) V_(L2) V_(L3) . . . V_(L31) V_(L32) V_(L33) . . . V_(L63)V_(L64) . . . V_(L512)

The value of each column in Table 2 is compared with the first thresholdvalue V_(th1), respectively. In Table 2, when the l^(th) valueV_(Ll)>V_(th1), it is determined that valid data is transmitted over thel^(th) sub-carrier; otherwise, when V_(Ll)≤V_(th1), it is determinedthat no valid data is transmitted over the l^(th) sub-carrier.

For example, if l=2, it is determined that valid data is transmittedover the 2^(nd) sub-carrier when V_(L2)>V_(th1). When V_(L2)≤V_(th1), itis determined that no valid data is transmitted over the 2^(nd)sub-carrier.

Similarly, after the value in each column of the output array of 1 rowand 512 columns is compared with the first threshold value V_(th1),respectively, 512 estimation results may be obtained.

When valid data is transmitted over the l^(th) sub-carrier, theestimation result may be set to 1; when no valid data is transmittedover the l^(th) sub-carrier, the estimation result may be set to 0; andfinally the data of 512 bits in length can be obtained. By reading 512bits of data, a bit of 1 is found therefrom. Valid data is transmittedover a sub-carrier corresponding to this bit.

To count the number of sub-carriers over which there is currently avalid data transmission, a bit by bit addition can be performed on the512 bits of data, and the obtained sum value is the number ofsub-carriers over which valid data is transmitted.

It can be seen from the above embodiments of the present disclosurethat, in a specific implementation, the N sub-carriers can also bedivided into k sub-carrier groups. For example, if 512 sub-carriers areequally divided into 16 sub-carrier groups, then each sub-carrier groupincludes 32 sub-carriers, where: the sub-carriers in the firstsub-carrier group are sub-carriers 1 to 32, the sub-carriers in thesecond sub-carrier group are sub-carriers 33˜64, and similarly, thesub-carriers in the 16^(th) sub-carrier group are sub-carriers 481˜512.

The average value for the m^(th) sub-carrier group is:V_(Rm)=(V_(L(1+((m−1)×32)))+V_(L(2+((m−1)×32)))+V_(L(3+((m−1)×32)))+ . .. +V_(L(m×32)))/32, 1≤m≤16. Then, the output array of 1 row and 512columns in Table 2 may be simplified into an output array of 1 row and16 columns, reference may be made to Table 3.

TABLE 3 V_(R1) V_(R2) V_(R3) . . . V_(R7) V_(R8) V_(R9) . . . V_(R16)

Average values corresponding to the 16 sub-carrier groups are comparedwith the second threshold V_(th2), respectively. When V_(Rm)>V_(th2), itis determined that valid data is transmitted over all sub-carriers inthe sub-carrier group; when V_(Rm)≤V_(th2), it is determined that novalid data is transmitted over any of the sub-carriers in thesub-carrier group.

For example, for the average value corresponding to the 1^(st)sub-carrier group, when V_(R1)>V_(th2), it is determined that valid datais transmitted over all 32 sub-carriers in the 1^(st) sub-carrier group,that is, the valid data is transmitted over sub-carriers 1˜32. For theaverage value corresponding to the 1^(st) sub-carrier group, whenV_(R1)≤V_(th2), it is determined that no valid data is transmitted overany of the 32 sub-carriers in the 1^(st) sub-carrier group, that is, novalid data is transmitted over any of the sub-carriers 1 to 32.

When it is estimated that valid data is transmitted over allsub-carriers in a certain sub-carrier group, each of the estimationresults of all the sub-carriers in the sub-carrier group may be set to1, that is, an all-ones number of 32 bits in length may be obtained.When it is estimated that no valid data is transmitted over any of thesub-carriers in a certain sub-carrier group, each of the estimationresults of all the sub-carriers in the sub-carrier group may be set to0, that is, an all-zeros number of 32 bits in length may be obtained.

With reference to FIG. 2, an embodiment of the present disclosureprovides a sub-carrier estimation apparatus 20 in a multi-carriercommunication system, including: a receiving unit 201, a trainingsequence extracting unit 202, a fast Fourier transform operation unit203, a multiplication unit 204, a real part extracting unit 205, acalculation unit 206 and an estimating unit 207.

The receiving unit 201 is configured to receive a data frame transmittedby a transmitting end.

The training sequence extracting unit 202 is configured to extract atraining sequence from the data frame.

The fast Fourier transform operation unit 203 is configured to perform afast Fourier transform operation on the training sequence and a presetreference sequence, respectively, to obtain frequency domain data of thetraining sequence and frequency domain data of the reference sequence.

The multiplication unit 204 is configured to conjugately multiply thefrequency domain data of the training sequence by the frequency domaindata of the reference sequence.

The real part extracting unit 205 is configured to extract a real partof a conjugate multiplication result, where the real part of theconjugate multiplication result is an M×N array, with M being the numberof symbols of the training sequence, and N being the number of points ofthe fast Fourier transform operation.

The calculation unit 206 is configured to average all values in eachcolumn of the M×N array, respectively, to obtain an output array of 1row and N columns.

The estimating unit 207 is configured to estimate, according to a valuein each column of the output array of 1 row and N columns, whether validdata is transmitted over N sub-carriers corresponding to the outputarray of 1 row and N columns.

In a specific implementation, the estimating unit 207 can be configuredto sequentially compare values in the output array of 1 row and Ncolumns with a first threshold that is preset; when the l^(th) value inthe output array of 1 row and N columns is greater than the firstthreshold, it is determined that the valid data is transmitted over thel^(th) sub-carrier of the N sub-carriers; and when the l^(th) value inthe output array of 1 row and N columns is not greater than the firstthreshold, it is determined that no valid data is transmitted over thel^(th) sub-carrier of the N sub-carriers; where 1≤l≤N.

In a specific implementation, the N sub-carriers can be divided into ksub-carrier groups, sub-carriers in any of the sub-carrier groups areadjacent to each other in a frequency domain, and there is nointersection between any two of the sub-carrier groups; the estimatingunit 207 can be configured to: acquire, from the output array of 1 rowand N columns, values corresponding to all sub-carriers in eachsub-carrier group, respectively; and estimate whether the valid data istransmitted over all sub-carriers in the each sub-carrier group,respectively.

In a specific implementation, the estimating unit 207 can be configuredto: calculate an average value for values corresponding to allsub-carriers in the each sub-carrier group, and compare the averagevalue with a second threshold that is preset; when the average value forthe values corresponding to all sub-carriers in the each sub-carriergroup is greater than the second threshold, it is determined that thevalid data is transmitted over all sub-carriers in the each sub-carriergroup; and when the average value for the values corresponding to allsub-carriers in the each sub-carrier group is not greater than thesecond threshold, it is determined that no valid data is transmittedover any of the sub-carriers in the each sub-carrier group.

In a specific implementation, the sub-carrier estimation apparatus 20 inthe multi-carrier communication system can further include: a countingunit (not shown in FIG. 2), configured to count the number of allsub-carriers, over which the valid data is transmitted, in the Nsub-carriers.

In a specific implementation, the sub-carrier estimation apparatus 20 inthe multi-carrier communication system can further include: asynchronization processing unit (not shown in FIG. 2), configured toperform synchronization processing on data in the data frame before thetraining sequence extracting unit extracts the training sequence fromthe data frame.

In a specific implementation, the training sequence includes any one of:a preamble sequence in the data frame for synchronization; or a datasequence that is preset in the data frame.

Persons of ordinary skill in the art may understand that, all or a partof the steps of the methods in the foregoing embodiments may beimplemented by a program instructing relevant hardware. The program maybe stored in a computer readable storage medium. The storage medium mayinclude: a ROM, a RAM, a magnetic disk, an optical disc, or the like.

Although the present disclosure has been disclosed above, it is notlimited thereto. Any person skilled in the art may make various changesand modifications without departing from the spirit and scope of thepresent disclosure. Therefore, the protection scope of the presentdisclosure shall be subject to the claims.

What is claimed is:
 1. A sub-carrier estimation method in amulti-carrier communication system, comprising: receiving a data frametransmitted by a transmitting end, and extracting a training sequencefrom the data frame; performing a fast Fourier transform operation onthe training sequence and a preset reference sequence, respectively, toobtain frequency domain data of the training sequence and frequencydomain data of the reference sequence, and conjugately multiplying thefrequency domain data of the training sequence by the frequency domaindata of the reference sequence; extracting a real part of a conjugatemultiplication result, wherein the real part of the conjugatemultiplication result is an M×N array, with M being the number ofsymbols of the training sequence, and N being the number of points ofthe fast Fourier transform operation; averaging all values in eachcolumn of the M×N array, respectively, to obtain an output array of 1row and N columns; and estimating, according to a value in each columnof the output array of 1 row and N columns, whether valid data istransmitted over N sub-carriers corresponding to the output array of 1row and N columns.
 2. The sub-carrier estimation method in themulti-carrier communication system according to claim 1, wherein theestimating, according to the value in each column of the output array of1 row and N columns, whether the valid data is transmitted over the Nsub-carriers corresponding to the output array of 1 row and N columnscomprises: sequentially comparing values in the output array of 1 rowand N columns with a first threshold that is preset; when an l^(th)value in the output array of 1 row and N columns is greater than thefirst threshold, it is determined that the valid data is transmittedover an l^(th) sub-carrier of the N sub-carriers; and when the l^(th)value in the output array of 1 row and N columns is not greater than thefirst threshold, it is determined that no valid data is transmitted overthe l^(th) sub-carrier of the N sub-carriers; wherein 1≤l≤N.
 3. Thesub-carrier estimation method in the multi-carrier communication systemaccording to claim 1, wherein the N sub-carriers are divided into ksub-carrier groups, sub-carriers in any of the sub-carrier groups areadjacent to each other in a frequency domain, and there is nointersection between any two of the sub-carrier groups; the estimating,according to the value in each column of the output array of 1 row and Ncolumns, whether the valid data is transmitted over the N sub-carrierscorresponding to the output array of 1 row and N columns comprises:acquiring, from the output array of 1 row and N columns, valuescorresponding to all sub-carriers in each sub-carrier group,respectively; and estimating whether the valid data is transmitted overall sub-carriers in the each sub-carrier group, respectively.
 4. Thesub-carrier estimation method in the multi-carrier communication systemaccording to claim 3, wherein the estimating whether the valid data istransmitted over all sub-carriers in the each sub-carrier group,respectively, comprises: calculating an average value for valuescorresponding to all sub-carriers in the each sub-carrier group, andcomparing the average value with a second threshold that is preset; whenthe average value for the values corresponding to all sub-carriers inthe each sub-carrier group is greater than the second threshold, it isdetermined that the valid data is transmitted over all sub-carriers inthe each sub-carrier group; and when the average value for the valuescorresponding to all sub-carriers in the each sub-carrier group is notgreater than the second threshold, it is determined that no valid datais transmitted over any of the sub-carriers in the each sub-carriergroup.
 5. The sub-carrier estimation method in the multi-carriercommunication system according to claim 1, wherein after the estimatingwhether the valid data is transmitted over the N sub-carrierscorresponding to the output array of 1 row and N columns, the methodfurther comprises: counting the number of sub-carriers, over which thevalid data is transmitted, in the N sub-carriers.
 6. The sub-carrierestimation method in the multi-carrier communication system according toclaim 2, wherein after the estimating whether the valid data istransmitted over the N sub-carriers corresponding to the output array of1 row and N columns, the method further comprises: counting the numberof sub-carriers, over which the valid data is transmitted, in the Nsub-carriers.
 7. The sub-carrier estimation method in the multi-carriercommunication system according to claim 3, wherein after the estimatingwhether the valid data is transmitted over the N sub-carrierscorresponding to the output array of 1 row and N columns, the methodfurther comprises: counting the number of sub-carriers, over which thevalid data is transmitted, in the N sub-carriers.
 8. The sub-carrierestimation method in the multi-carrier communication system according toclaim 4, wherein after the estimating whether the valid data istransmitted over the N sub-carriers corresponding to the output array of1 row and N columns, the method further comprises: counting the numberof sub-carriers, over which the valid data is transmitted, in the Nsub-carriers.
 9. The sub-carrier estimation method in the multi-carriercommunication system according to claim 1, wherein before the extractingthe training sequence from the data frame, the method further comprises:performing synchronization processing on data in the data frame.
 10. Thesub-carrier estimation method in the multi-carrier communication systemaccording to claim 9, wherein the training sequence comprises any oneof: a preamble sequence in the data frame for synchronization; or a datasequence that is preset in the data frame.
 11. A sub-carrier estimationapparatus in a multi-carrier communication system, comprising: areceiving unit, configured to receive a data frame transmitted by atransmitting end; a training sequence extracting unit, configured toextract a training sequence from the data frame; a fast Fouriertransform operation unit, configured to perform a fast Fourier transformoperation on the training sequence and a preset reference sequence,respectively, to obtain frequency domain data of the training sequenceand frequency domain data of the reference sequence; a multiplicationunit, configured to conjugately multiply the frequency domain data ofthe training sequence by the frequency domain data of the referencesequence; a real part extracting unit, configured to extract a real partof a conjugate multiplication result, wherein the real part of theconjugate multiplication result is an M×N array, with M being the numberof symbols of the training sequence, and N being the number of points ofthe fast Fourier transform operation; a calculation unit, configured toaverage all values in each column of the M×N array, respectively, toobtain an output array of 1 row and N columns; and an estimating unit,configured to estimate, according to a value in each column of theoutput array of 1 row and N columns, whether valid data is transmittedover N sub-carriers corresponding to the output array of 1 row and Ncolumns.
 12. The sub-carrier estimation apparatus in the multi-carriercommunication system according to claim 11, wherein the estimating unitis configured to sequentially compare values in the output array of 1row and N columns with a first threshold that is preset; when an l^(th)value in the output array of 1 row and N columns is greater than thefirst threshold, it is determined that the valid data is transmittedover an l^(th) sub-carrier of the N sub-carriers; and when the l^(th)value in the output array of 1 row and N columns is not greater than thefirst threshold, it is determined that no valid data is transmitted overthe l^(th) sub-carrier of the N sub-carriers; wherein 1≤l≤N.
 13. Thesub-carrier estimation device in the multi-carrier communication systemaccording to claim 11, wherein the N sub-carriers are divided into ksub-carrier groups, sub-carriers in any of the sub-carrier groups areadjacent to each other in a frequency domain, and there is nointersection between any two of the sub-carrier groups; the estimatingunit is configured to: acquire, from the output array of 1 row and Ncolumns, values corresponding to all sub-carriers in each sub-carriergroup, respectively; and estimate whether the valid data is transmittedover all sub-carriers in the each sub-carrier group, respectively. 14.The sub-carrier estimation apparatus in the multi-carrier communicationsystem according to claim 13, wherein the estimating unit is furtherconfigured to: calculate an average value for values corresponding toall sub-carriers in the each sub-carrier group, and compare the averagevalue with a second threshold that is preset; when the average value forthe values corresponding to all sub-carriers in the each sub-carriergroup is greater than the second threshold, it is determined that thevalid data is transmitted over all sub-carriers in the each sub-carriergroup; and when the average value for the values corresponding to allsub-carriers in the each sub-carrier group is not greater than thesecond threshold, it is determined that no valid data is transmittedover all sub-carriers in the each sub-carrier group.
 15. The sub-carrierestimation apparatus in the multi-carrier communication system accordingto claim 11, further comprising: a counting unit, configured to countthe number of sub-carriers, over which the valid data is transmitted, inthe N sub-carriers.
 16. The sub-carrier estimation apparatus in themulti-carrier communication system according to claim 12, furthercomprising: a counting unit, configured to count the number ofsub-carriers, over which the valid data is transmitted, in the Nsub-carriers.
 17. The sub-carrier estimation apparatus in themulti-carrier communication system according to claim 13, furthercomprising: a counting unit, configured to count the number ofsub-carriers, over which the valid data is transmitted, in the Nsub-carriers.
 18. The sub-carrier estimation apparatus in themulti-carrier communication system according to claim 14, furthercomprising: a counting unit, configured to count the number ofsub-carriers, over which the valid data is transmitted, in the Nsub-carriers.
 19. The sub-carrier estimation apparatus in themulti-carrier communication system according to claim 11, furthercomprising: a synchronization processing unit, configured to performsynchronization processing on data in the data frame before the trainingsequence extracting unit extracts the training sequence from the dataframe.
 20. The sub-carrier estimation apparatus in the multi-carriercommunication system according to claim 19, wherein the trainingsequence comprises any one of: a preamble sequence in the data frame forsynchronization; or a data sequence that is preset in the data frame.